Neuroglycopenia is the clinical state of brain sugar deficiency. The condition is rare, and the investigator (Dr. DeVivo) and his team at Columbia are recognized internationally. They are trying to determine the genetic basis for the condition and to develop better forms of treatment. This study hopes to enroll 40 subjects. The patients are admitted to the GCRC for procedures, including a routine brain wave followed by continuous brain wave monitoring using a cable telemetry system. This system permits continuous brain wave recording and video taping of the patient for a period of 24 hours. A blood specimen will be obtained (approximately 1 tablespoon) to measure various blood chemistries and to search for genetic mutations involving the glucose transporter gene. A urine specimen will be analyzed for organic acids. A skin biopsy will be performed in the patient's room. The area of the skin is numbed with local anesthetic to minimize any pain or discomfort. The associated risks are minimal. Neuropsychological testing will be performed to evaluate the patient's cognitive abilities and behavior. The patients will return annually for an abbreviated evaluation. The clinical examination and the neuropsychological evaluation will be repeated. On the final visit, patients will be asked to undergo a functional MRI to evaluate the ability of the patient's brain to sustain a metabolic function for a period of time.